Serotiny in the South African shrub Protea repens is associated with gradients of precipitation, temperature, and fire intensity

Abstract

Globally, variability in canopy seed retention within closed cones (serotiny) among fire-adapted plant species is often associated with gradients in fire regime. Few studies have investigated the association of intraspecific variation in serotiny with geographical variation in fire and other environmental factors, especially climatic ones, and none has done so in the Cape Floristic Region (CFR) of South Africa. Yet the relationship between environmental gradients and intraspecific variation in reproductive traits may help us understand if those gradients partly shaped the evolution of the rich diversity or proteas in the CFR, and predict the resilience of fire-adapted Protea species to climate and fire regime changes in the CFR. We examined the association of the variability in serotiny in Protea repens (L.) L, the Common Sugarbush, with gradients in fire regime and climatic factors, and with plant age, cone age, and age of oldest closed cone across its 700 km-long longitudinal range in the CFR. Cone age was a significant covariate of the probability that a given cone was closed (our measure of serotiny), but plant age and age of oldest closed cone were not. Variability in the degree of serotiny was significant among populations. Serotiny was highest where fire intensity was historically high, where both mean annual precipitation and mean annual temperature were low, and where rainfall was least seasonal, but fire frequency was not a predictor of serotiny.

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Acknowledgements

We thank Jasper Slingsby, Tony Rebelo, Tom Slingsby, and Nick Lindenberg for their help. Kobus Kellerman and Jocelyne de Gouvenain assisted with the field sampling. Jane Carlson generously provided UTM coordinates of P. repens populations. John Silander Jr. reviewed the draft manuscript. We thank CapeNature, the Eastern Cape Parks and Tourism Agency, and the South African National Parks for permission to sample populations of P. repens under their jurisdiction. RdG thanks the University of Cape Town Biological Sciences Department for in-kind support and JM’s hospitality while conducting sabbatical research in his lab. We thank three anonymous reviewers for their thorough and constructive comments.